As Florida Keys residents confront rising sea levels, what lessons?

On many mornings over the past 22 years, the Rev. Tony Mullane has pulled back his bedroom curtains and watched endangered Key deer roaming the grounds of St. Peter Catholic Church. He considers the free nature show one of the bonuses of his ministry in the Florida Keys.

On other days, however, there are no deer to be seen – only water from the Straits of Florida lapping perilously near to the church buildings.

"It does come close to the church in a high tide," says Father Tony, as he's known. "There's a gravel pit behind us that's supposed to be a natural buffer from the water of Coupon Bight, but it fills, and sometimes laps over into, the church grounds."

What is happening at St. Peter is being repeated across the length of the 125-mile, low-lying island chain off Florida's south coast. Average sea levels on the islands are already nine inches higher than a century ago, according to environmental studies. Flooding has become much more common, which has prompted local officials and others to explore remedies. But in some cases, just how the islanders should proceed is still being figured out. (Read here to learn how the Netherlands have fought rising sea levels.)

"High tides are higher today, reaching farther inland than they did in the past. And the frequency of tides high enough to flood streets and salt-sensitive natural areas is greater," says Chris Bergh, director of the Nature Conservancy's Florida Keys program, who cites both his own observations and data from the National Oceanic and Atmospheric Administration.

"Some change is inevitable," adds Mr. Bergh, who lives on Big Pine Key with his wife, Elizabeth, and son, Nate. "It's how we adapt to that change and manage it to our best advantage."

Of course, the Florida Keys aren't the only low-lying places in the United States. People in plenty of other coastal areas are keeping an eye on the sea level – and are concerned about the future.

But the Keys' delicate ecosystem and unique geography make them of particular interest to global-warming observers, and the islands have become a "canary in a coal mine" – an indicator of what other areas might need to prepare for. (Read here to learn about the Keys' special environmental designation.)

"The Keys are a very visible example of the effects of an irregular but persistent sea-level rise that we have seen since the Industrial Revolution," says Prof. Harold Wanless, chair of geological sciences at the University of Miami.

Bergh and fellow researchers recently completed an evaluation of existing climate-change data, and they produced an alarming study containing several scenarios for the Keys during the rest of the century. Across the Keys in a best-case scenario, the study suggested, the sea would rise seven inches by 2100, which could wipe $11 billion from property values. In the worst-case scenario, the sea would rise 55 inches by 2100, with 5,950 acres lost on Big Pine alone. Property values over all the islands could take a hit of more than $35.1 billion.

"Even if we get our act together – if we all stop polluting with greenhouse gases, we stop deforestation, and the population stops growing – there's still going to be a lag," Bergh says.

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